ESSAY BEYOND THE IVORY TOWER This year's essay series highlights the benefits that scientists, science, The Scientific Consensus and technology have brought to society throughout history. on Climate Change Naomi Oreskes climate change is natural. However, none olicy-makers and the media, particular- Academy of Sciences report, Climate of these papers argued that point. ly in the United States, frequently assert Change Science: An Analysis of Some Key This analysis shows that scientists publish- Pthat climate science is highly uncertain. Questions, begins: “Greenhouse gases are ing in the peer-reviewed literature agree with Some have used this as an argument against accumulating in Earth’s atmosphere as a re- IPCC, the National Academy of Sciences, and adopting strong measures to reduce green- sult of human activities, causing surface air the public statements of their professional so- house gas emissions. For example, while dis- temperatures and subsurface ocean temper- cieties. Politicians, economists, journalists, cussing a major U.S. Environmental Pro- atures to rise” [p. 1 in (5)]. The report ex- and others may have the impression of confu- tection Agency report on the risks of climate plicitly asks whether the IPCC assessment is sion, disagreement, or discord among climate change, then–EPA administrator Christine a fair summary of professional scientific scientists, but that impression is incorrect. Whitman argued, “As [the report] went thinking, and answers yes: “The IPCC’s The scientific consensus might, of through review, there conclusion that most of the course, be wrong. If the history of science was less consensus on Without substantial disagreement, observed warming of the teaches anything, it is humility, and no one the science and conclu- scientists find human activities last 50 years is likely to can be faulted for failing to act on what is sions on climate change” are heating the Earth’s surface. have been due to the in- not known. But our grandchildren will (1). Some corporations crease in greenhouse gas surely blame us if they find that we under- whose revenues might concentrations accurately stood the reality of anthropogenic climate be adversely affected by controls on carbon reflects the current thinking of the scientific change and failed to do anything about it. dioxide emissions have also alleged major community on this issue” [p. 3 in (5)]. Many details about climate interactions uncertainties in the science (2). Such state- Others agree. The American Meteoro- are not well understood, and there are am- ments suggest that there might be substantive logical Society (6), the American Geo- ple grounds for continued research to pro- disagreement in the scientific community physical Union (7), and the American vide a better basis for understanding cli- about the reality of anthropogenic climate Association for the Advancement of Science mate dynamics. The question of what to do change. This is not the case. (AAAS) all have issued statements in recent about climate change is also still open. But The scientific consensus is clearly ex- years concluding that the evidence for human there is a scientific consensus on the reality pressed in the reports of the Inter- modification of climate is compelling (8). of anthropogenic climate change. Climate governmental Panel on Climate Change The drafting of such reports and state- scientists have repeatedly tried to make this (IPCC). Created in 1988 by the World ments involves many opportunities for clear. It is time for the rest of us to listen. Meteorological Organization and the United comment, criticism, and revision, and it is Nations Environmental Programme, IPCC’s not likely that they would diverge greatly References and Notes purpose is to evaluate the state of climate sci- from the opinions of the societies’ mem- 1. A. C. Revkin, K. Q. Seelye, New York Times, 19 June 2003, A1. ence as a basis for informed policy action, bers. Nevertheless, they might downplay 2. S. van den Hove, M. Le Menestrel, H.-C. de Bettignies, primarily on the basis of peer-reviewed and legitimate dissenting opinions. That hy- Climate Policy 2 (1), 3 (2003). 3. See www.ipcc.ch/about/about.htm. published scientific literature (3). In its most pothesis was tested by analyzing 928 ab- 4. J. J. McCarthy et al., Eds., Climate Change 2001: recent assessment, IPCC states unequivocal- stracts, published in refereed scientific Impacts, Adaptation, and Vulnerability (Cambridge ly that the consensus of scientific opinion is journals between 1993 and 2003, and list- Univ. Press, Cambridge, 2001). 5. National Academy of Sciences Committee on the that Earth’s climate is being affected by hu- ed in the ISI database with the keywords Science of Climate Change, Climate Change Science: man activities: “Human activities … are “climate change” (9). An Analysis of Some Key Questions (National Academy Press, Washington, DC, 2001). modifying the concentration of atmospheric The 928 papers were divided into six cat- 6. American Meteorological Society, Bull. Am. Meteorol. constituents … that absorb or scatter radiant egories: explicit endorsement of the consen- Soc. 84, 508 (2003). energy. [M]ost of the observed warming sus position, evaluation of impacts, mitiga- 7. American Geophysical Union, Eos 84 (51), 574 (2003). … 8. See www.ourplanet.com/aaas/pages/atmos02.html. over the last 50 years is likely to have been tion proposals, methods, paleoclimate 9. The first year for which the database consistently due to the increase in greenhouse gas con- analysis, and rejection of the consensus po- published abstracts was 1993. Some abstracts were deleted from our analysis because, although the au- centrations” [p. 21 in (4)]. sition. Of all the papers, 75% fell into the thors had put “climate change” in their key words, the IPCC is not alone in its conclusions. In first three categories, either explicitly or im- paper was not about climate change. recent years, all major scientific bodies in plicitly accepting the consensus view; 25% 10. This essay is excerpted from the 2004 George Sarton Memorial Lecture, “Consensus in science: How do we the United States whose members’ expertise dealt with methods or paleoclimate, taking know we’re not wrong,” presented at the AAAS meet- bears directly on the matter have issued sim- no position on current anthropogenic cli- ing on 13 February 2004. I am grateful to AAAS and the History of Science Society for their support of ilar statements. For example, the National mate change. Remarkably, none of the pa- this lectureship; to my research assistants S. Luis and pers disagreed with the consensus position. G. Law; and to D. C. Agnew, K. Belitz, J. R. Fleming, M. Admittedly, authors evaluating impacts, T. Greene, H. Leifert, and R. C. J. Somerville for helpful The author is in the Department of History and Science discussions. Studies Program, University of California at San Diego, developing methods, or studying paleocli- La Jolla, CA 92093, USA. E-mail: [email protected] matic change might believe that current 10.1126/science.1103618

1686 3 DECEMBER 2004 VOL 306 SCIENCE www.sciencemag.org Published by AAAS